Role of oxide barrier in intergranular tunnel junctions: An enhanced magnetoresistance in Si O2 and ZnO coated Fe3 O4 nanoparticle compacts

A systematic study of oxide coated magnetic nanoparticles is carried out to understand and evaluate the effect of oxide tunnel barrier on the magnetoresistance (MR) of magnetite core-shell nanocompacts. Si O2 and ZnO coated Fe3 O4 nanoparticles with a shell thickness of ∼2 nm have been synthesized and characterized. Magnetic measurements on oxide coated Fe3 O4 nanoparticles reveal blocking behavior and superparamagnetism below ∼200 K. The magnitude of electrical resistivity at room temperature of Si O2 and ZnO coated Fe3 O4 compacts is found to be two to five orders higher than that of pure nanocrystalline Fe3 O4 compacts due to resulting insulating oxide layer between magnetite domains. For these nanocompacts, large low field magnetoresistances of -11.5% and -5.8% are achieved in an applied magnetic field of 1 T at 100 K that could have origins of spin-dependent tunnel MR across the nanometric granules of Fe3 O4 safely embedded in insulating oxide matrix. © 2008 American Institute of Physics.